1道方程组

求方程组:
x-y-z=5 ........[1]
y-x-z=1 ........[2]
z-x-y=-15............[3]

[1]+[2]:
-2z=6
z=-3

[2]+[3]:
-2x=-14
x=7
z=-15+x+y=-15+7-3=-11

X＝7、Y＝5、Z＝－3

设三个式子分别为(1)(2)(3)式
-((1)+(2)+(3))得x+y+z=9......(4)
1/2((1)+(4))得x=7
1/2((2)+(4))得y=5
1/2((3)+(4))得z=-3

x=-8
y=-10
z=-3